Electron discharge device



1958 R. G. O'FALLON 2,850,273

ELECTRON DISCHARGE DEVICE Filed Dec. 30, 1955 EGUIPOTENTIAL LINESEGUIPOTENTIAL LINES IN VEN TOR.

MTdCZOTQZZOm g 44 i M United States Patent 9 M ELECTRON DISQHARGE DEVICERichard G. OFallon, Westchester, Ill., assignor to Motorola, lino,Chicago, lllh, a corporation of Iilinois Application December 30, 1%5,Serial No. 556,635

1 Claim. (Cl. Mfr-299) The present invention relates to electrondischarge devices and more particularly to a power tube that eXhibitsfavorable characteristics of a pentode type and yet which incorporatesmore economical structure of the beam type.

The pcntode power tube includes a well-known suppressor grid between thescreen grid and plate electrodes of that tube, The suppressor is usuallyoperated at cathode or ground potential, and it opposes the flow ofsecondary electrons from the plate to the screen which occurs in theusual tetrode. This opposition is due to the fact thata n electrostaticfield with a negative potential gradient is established in the vicinityof the plate, and this field returns the secondary electrons to theplate. This results in eliminating distortions in the plate-current vs.plate-voltage tube characteristics.

The beam power tube has been developed in an effort to. duplicate theimproved pentode characteristics with a tetrode type of structure. Inthe beam power, tube, the electrons move from an elongated cathode to asurroundinganode in a series of sheet-like beams, and these beamsfunction as an effective suppressor in the space between the screen gridand the anode due to the mutual repulsion between the electrons. Thatis, the beams themselves estahlish the needed negative potentialgradient around the anode to return the secondary electrons thereto.

It is usual to construct beam power tubes with an essentially fiattwo-sidedelongated cathode, with one set of beams emanating from oneside of the cathode and traveling in one direction to the anode, andwith another set of beams emanating from the other side of the cathodeand traveling in the opposite'direction to the anode.

It has been found with beam power tubes of this type that it isdifficult to duplicate the improved characteristics of the pentode, anddiscontinuities usually appear in the respective knee portions of itsplate-current vs. plate voltage characteristic curves. especiallytroublesome when the tube feeds into a resonant output circuit sincethere is a tendency to set up parasitic oscillations in the outputcircuit. These discontinuiticsare due to the focusing effects of thebeam-formi sst qtls n the ube 911 h s e y directed 61w tron beams in thetwo halves of the tube. In a manner to be explained, the beam formingelectrodes set up electrostatic fields thathaye a tendency to producefocusing effects on the beams, and due to the difiiculty in obtainingabsolutely symmetrical structure on both sides of the tube, thesefocusing effects are different for the different beams and this producesthe discontinuities in the above-mentioned characteristics and theresulting parasitic oscillations in the output circuit.

It is, accordingly, an object of the present invention to provide animproved electron discharge device of the beam power type which is notsubject to the above-described disadvantages inherent in the prior artdevices of this general type.

Another object of the invention is to provide such an improved beampower electron discharge device in which defects in the focusingeflfects of the beam-forming elec- These discontinuities are 2,860,273Patented Nov. 11, 1958 trodes within the tube are obviated for allpractical purposes so as to improve the operating characteristics of thetube and to prevent undesired parasitic oscillations in the outputcircuit thereof.

A feature of the invention is the provision in an im: proved electrondischarge device of the beam power type of one or more auxiliary wireelectrodes established at the potential of the beam-forming electrodesand extending across the apertures or windows formed by these elec:trodes, so as to oppose adverse focusing efiects within the tube,thereby to improve the translating charac: teristics of the dischargedevice.

The above and other features of the invention are believed to be new areexpressly set forth in the claims. The invention itself, however,together with further obiects and advantages thereof, may be best understood by reference to the following description when, taken inconjunction with the accompanying drawing in which: i

Fig. l is a perspective schematic representation of a typical prior artbeam power tube;

Fig. 2 shows schematically the electrostatic field set up in one half ofthe tube of Fig. 1;

Figs. 3 and 4 are representations of the tube of Fig. 1 modified inaccordance with the invention;

' Pig. 5 is a schematic representation of the electrostatic field set upin half of the modified tube of. the present inventiong and Fig. 6' is acut-away view of the modified tube of the invention. i i i The inventionprovides an, electron discharge device of the beam type which comprisesa cathode adapted to emit electrons from opposite sides thereof, ananode structure having a first portion facing and spa ced frorn one sideof the cathode and a second portionfacing and spaced from the other sideof the cathode, a grid structure interposed between the cathode and theanode, and a beam-forming structure interposed between the'gridstructure and the anode for forming the electrons from the oppositesides of the cathode into a pair of oppositely directed beams. Thebeam-forming structure has a pair of apertures or Windows through whichrespective ones of the beamstravel to the anode. Thecathode andbeam-forming structure are established at reference po: tential, and thegrid and anode are established at different positive potentials duringnormal operation of the device. This causes electrostatic fields to be"established in the windows of the beamforming structure and these fieldshave a tendency to focus the respective beams in an asymmetrical mannerand produce adverse operating characteristics in the tube. In accordancewith the invention, at least one auxiliary electrode is positioned ineach of the windows in the beam-forming structure and these auxiliaryelectrodes are established at the reference potential of the cathode andbeam-forming electrodes to distort the electrostatic fields in such amanner that the beam focusing tendency of these fields is reduced toeliminate the abovementioned distortions.

The electron discharge device of Fig. 1 includes an elongatedessentially flat cathode 10 which is adapted to emit electrons from eachof its opposite faces. The cathode is surrounded by a spirally-wound,wire, grid structure 11 which funcitions as the control grid; andstructure if is in turn surrounded by a similar spirallywound, wire,grid structure 12 which funcitions as the screen grid. The elements 10,11 and 12 are, themselves, surrounded by an essentiallyrectangular-shaped anode l3, which has a first portion 13a facing oneside of the cathode and a second portion 13b facing the other side ofthe cathode. in the form of a pair of beam-forming electrodes 14 and 15are disposed on opposite sides of the screen grid,

A beam-forming structure and these electrodes define an aperture orwindow between each side of cathode and the respective portions 13a, 13bof anode 13,

' During normal operation of the tube, the cathode 10 and beam formingelectrodes 14, are established at a reference potential such as ground,and the screen electrode 12 and anode 13 are established at differentpositive potentials. For example, the screen electrode may beestablished at +150 volts direct current and the anode may beestablished at +60 volts direct current. The assembly is such that theelectrons emitted by one side of the cathode 10 are formed into a firstseries of sheet-like beams directed at the anode portion 13a, and theelectrons emitted from the other side are formed into a second series ofsheet-like beams directed at the anode. portion 1312. For convenience ofdescription, each of these series will be referred to herein as but asingle beam.

The electrostatic field set up in one of the windows of the beam-formingelectrodes 14, 15 is shown in Fig. 2. As noted previously, the anodeportion 13a is established at a positive direct-current voltage of, forexample, 60 volts; the beam-forming electrodes 14, 15 are established atreference or ground voltage; and the screen electrode 12 is establishedat a positive direct-current voltage of, for example, 150 volts. Theseelements set up an electrostatic field in the aperture 'or window of thebeam-forming electrodes 14, 15 as represented by the equi-potentiallines a, b, c and d. The shape of these lines in is such that the beamhas a tendency to be defocused as it travels between the screenelectrode and the window in the beam-forming electrodes and to befocused as it travels between the beam-forming electrodes and the anodeportion 13a. A different defocusing and focusing effect is experiencedby the oppositely-directed beam passing through the other window of thebeam-forming electrodes 14, 15 to anode portion 13b. These differentfocusing effects of the electro static fields within the two halves ofthe tube produce discontinuities at the respective knee portions of theplate-current vs. plate-voltage characteristic curves of the tube, andthis produces the undesired effects discussed previously herein.

In short, although the beam power tube attempts to achieve the desiredoperating characteristics of the pentode, the prior art tubes of thisgeneral type have fallen short of this goal and still exhibitcharacteristics similar to those of the usual tetrode.

In accordance with the present invention, one or more auxiliaryelectrodes 16, preferably in the form of thin wires, are positionedwithin each of the windows in the beam forming structure 14, 15. Theseauxiliary electrodes extend preferably along the longitudinal axis ofthese windows essentially parallel to the longitudinal axis of thecathode 10. As shown in Fig. 4, the auxiliary electrodes 16 areestablished at the potential of the beam-forming electrodes and thecathode. These auxiliary electrodes distort the electrostatic field ineach of the windows in the beam-forming electrodes to oppose thefocusing tendency of these fields.

As shown m Fig.

5, for example, the auxiliary electrode 16 has a tendency to straightenout the equi-potential lines a, b, c and d of Fig. 2 to produce thelines e, f, g and it that have substantially less focusing effect on thebeam so that the undesired results of such focusing are overcome for allpractical purposes.

As previously noted, the windows in the beam forming electrodes areelongated and extend essentially parallel to the respective oppositefaces of the cathode. The auxiliary electrodes 16 may conveniently beformed by welding wires to the beam forming electrodes so that theyextend across each of the windows essentially parallel to the cathode.

Therefore, in accordance with the present invention, one or moreauxiliary suppressor electrodes in the form of the wires 16 are insertedin each of the windows of the beam-forming electrodes effectively toconvert the beam power tetrode into a pentode insofar as its operationis concerned, so that the improved operating characteristics of thepentode may be obtained while still retaining the mechanical economiesof the beam power tetrode.

I claim:

An electron discharge device of the beam type subject to exhibit anirregularity in the anode current-anode voltage characteristic curvewhen the anode potential is at a low positive potential with respect tothe cathode and below the screen grid potential, including incombination an envelope for said device, an elongated cathode having apair of opposite faces adapted to emit electrons therefrom, an anodeelectrode surrounding said cathode and. spaced therefrom, control andscreen grid electrodes surrounding said cathode and interposed in theorder named between said cathode and said anode, a beam formingstructure interposed between said screen grid electrode and said anode,said beam forming structure having a pair of elongated windows one ofwhich is associated with each of the faces of said cathode, meanscoupling said beam forming structure directly to said cathode forestablishing the same 'at a common potential, and a conductor wirecentrally positioned in each of said elongated windows and substantiallyin the plane thereof, such conductor wires extending longitudinally ofsaid windows and being substantially parallel to said elongated cathode,said conductor wires being supported by said beam forming structure anddirectly electrically connected thereto internally of said envelope forestablishing the same at a common potential, thereby modifying theelectrostatic field through which the electrons travel from said screengrid electrode to said anode electrode.

References Cited in the file of this patent UNITED STATES PATENTS2,146,016 Herold Feb. 7, 1939 2,235,817 Freeman Mar. 25, 1941 2,599,629Grimm June 10, 1952 FOREIGN PATENTS 869,693 France Nov. 17, 1941

